U2 Lecture 6 Flashcards
- Describe the dietary factors that influence bone - Describe the roles of calcitonin and parathyroid hormone in the regulation of blood calcium - describe the vitamin D pathway, and the role of calcitriol in calcium homeostasis - Describe the role of dietary calcium in maintenance of bone mass and know the recommended allowance for calcium intake for young adults - Describe the role of growth hormone and sex hormones in modulating bone mass - Describe the skeletal disorders that arise fro
What factors affect bone density?
Diet, hormones and exercise
What are the dietary categories that affect bone density?
Minerals and Vitamins
What minerals affect bone density?
Calcium and phosphorus (also magnesium, fluoride, and manganese)
What vitamins affect bone density?
Vitamin A, C, D, K B12
What does vitamin A do?
Stimulates activity of osetoblasts
What does vitamin C do?
Needed for collagen synthesis
What does vitamin D do?
Stimulates calcium absorption
What does vitamin K, B12 do?
Needed for synthesis of bone proteins
Define calcium homeostasis
Maintaining adequate calcium levels in the body
Normal Range: 8.5 - 11 mg/dL
Why is calcium homeostasis important?
Membrane excitability, blood clotting and intracellular activity (second messenger
How does the body control calcium entry and exit from blood?
Through level of storage in bone, through level of kidney excretion, and through intestinal absorption levels
Extracellular fluid Ca2+ represents how much of total body calcium?
1% but it is highly regulated
What hormones are involved in calcium homeostasis?
Calcitonin, Parathyroid hormone, and calcitriol (Vitamin D)
What type of molecule is Calcitonin?
Polar with H bonding
Calcitonin stimulus
High blood calcium
Calcitonin source
Thyroid gland (parafollicular cells “C cells”)
Calcitonin target tissues
Bone, kidney, and intestine
Calcitonin actions
Goal: DECREASE blood Ca2+ concentration
- inhibits osetoclast activity (decreased bone resorption)
- increases excretion of calcium at kidney
- inhibits intestinal absorption of calcium
Calcitonin end result
DECREASE in blood calcium concentration
What type of molecule is the parathyroid hormone?
Polar
Parathyroid hormone stimulus
Low blood calcium
Parathyroid hormone source
Parathyroid gland
Parathyroid hormone target tissues
Bone, kidney, intestine
Parathyroid hormone actions
Goal: INCREASE blood Ca2+ concentration
- stimulates osteoclast activity (increased bone resorption)
- Decreases excretion of calcium at kidney
- stimulates intestinal absorption of calcium and promotes calcitriol (active vit. D) action
Parathyroid hormone end result
INCREASE blood calcium concentration
Define negative feedback
When levels inside the body get too extreme, the body counter acts them and does the opposite
Negative feedback regulation of blood Ca2+ concentration
When blood calcium levels get too high, calcitonin is released
When blood calcium levels get too low, Parathyroid hormone is released
What type of molecule is Calcitriol
Calcitriol is active vitamin D
- Very non-polar
- hydrophobic
- fat soluble
- steroid hormone- derived from cholesterol (lipophillic / hydrophobic)
Vitamin D pathway
- Starts in 2 places: skin or intestine
- Skin - light hits vit. D in skin then turns it into vit. D3. Then goes through blood to liver
- Intestine - get dietary vit. D3 from fish oil, egg yolk, milk and goes straight to liver through blood
- In liver, all vit. D3 turns into 25-hydroxycholecalciferol
- goes through blood again to kidney where the active form of vit. D is (calcitriol), PTH will increase levels of Ca2+ if there’s low blood calcium
Calcitriol stimulates
It stimulates osetoclast activity (bone resorption)
Calcitriol actions
- Decreases calcium excretion at the kidney
- Increases calcium absorption at the intestine (works well with PTH to stimulate absorption)
Calcitriol end result
INCREASE blood calcium
What is the recommended Ca2+ intake for young adults?
1000 mg to avoid bone loss
What hormones act on osteoclasts?
Calcitonin and parathyroid hormone
What hormones act on osteoblasts?
growth hormone (sometotropin) and estrogen/ testosterone
Growth Hormone (GH or Somatotropin)
- stimulates cell growth and protein synthesis (collagen)
- stimulates formation of insulin like growth factors (IGF’s) -> stimulates osteoblast activity -> stimulates bone formation
Skeletal disorders associated with GH
Pituitary dwarfism, pituitary gigantism, acromegaly
Pituitary dwarfism
decrease in GH, slow epiphyseal growth
Pituitary gigantism
increase in GH, high epiphyseal growth
Acromegaly
Increase in GH after puberty, thickening of bone
Estrogen and Testosterone
- Both stimulate osteoblast activity -> stimulate bone formation
- Levels increase at puberty: bone growth/ spurts, eventually cause closure of epiphyseal plates bc osteoblast/osteoclast activity is greater than chondrocyte activity
- levels decrease with old age
